Chronic kidney disease (CKD) affects over 20 million persons in the U.S. and is an independent risk factor for cerebrovascular disease including stroke, microbleeds and cognitive impairment. The intestinal microbial population is altered in CKD and there is increased production of bacterial-derived uremic toxins such as indoxyl sulfate, p-cresyl sulfate and trimethylamine N-oxide (TMAO). These toxins translocate into the bloodstream and induce systemic inflammation and oxidative stress, and have been shown to disrupt the endothelial barrier in vitro. Population studies have noted an association between higher levels of gut bacterial- derived uremic toxins with increased risk of cardiovascular morbidity and CKD progression. The current proposal examines the kidney-gut-brain axis: how uremic toxins from intestinal microbes contribute to brain microbleeds in CKD. Microbleeds are an important predictor of future stroke and cognitive decline, and are more common in CKD patients than in age-matched controls. Our central hypothesis is that indoxyl sulfate, p-cresyl sulfate and TMAO induce oxidative stress, microglial activation and breakdown of cell-cell tight junctions, leading to compromised blood-brain barrier integrity and microbleeds formation. Our project will utilize interventions that raise or lower systemic levels of gut-derived uremic toxins in mice to study brain microbleeds formation. Our research group has the necessary tools and expertise to complete the proposed work including microbial 16S rRNA sequencing technology, small animal brain magnetic resonance imaging, mass spectrometry, and bioinformatics personnel. Our Specific Aims are as follows: Specific Aim 1: To determine the role of gut-derived uremic toxins on microbleeds formation in vivo. Specific Aim 2: To determine the effects of lowering specific gut-derived uremic toxins on brain microbleeds pathophysiology in vivo. We expect that our work will have an important positive impact by guiding the development of gut-directed therapies to modify the CKD-cerebrovascular relationship.